A problem with heat pumps, especially solid state heat pumps, is that thermal expansion and contraction during use can damage the material from which the pump is made. This problem is typically exacerbated with scale thereby limiting the size of the heat pump and therefore its usefulness.
For example, a thermoelectric cooler (TEC) may comprise stacked layers of semiconductor or equivalent heat pumping elements in between thin ceramic plates. The ceramic material has a propensity for internal thermal expansion that can cause fracturing of the ceramic, which dictates a maximum size of the area of the ceramic layer that should be used for the manufacture of TECs. For multilayer TECs this is typically in the region of 45 mm×45 mm.
The limit on the ceramic layer size restricts the number of semiconductor pillars that can be fitted in an array between layers and ultimately limits the maximum heat pumping capacity of the TEC device. In applications where the heat pumping capacity of a single TEC device is not sufficient, a heat pumping structure comprising multiple TEC devices can be used. However, thermal expansion and contraction of the device being cooled can damage the heat pumping structure.
For example, in the case where the device being cooled is an image sensor, multiple TEC devices may be used in parallel to remove heat from the image sensor. However, as the image sensor is cooled it shrinks as a result of thermal contraction and this can cause a mechanical fracture in the heat pumping structure, resulting in degradation or total failure in cooling performance.
Addressing these problems is complicated for applications where the device to be cooled needs to operate in a vacuum since the use of gases and lubricants is to be avoided.
It would be desirable to provide a heat pump system that mitigates the problems outlined above.